1. Field of the Invention
The present invention pertains to a coiled tubing injection apparatus for inserting and removing a continuous length of tubing with respect to a well.
2. Background
In the development and production of subterranean hydrocarbon deposits and other energy sources there are many occasions when it is necessary to insert an elongated tube from the surface deep into the well from various purposes including, injection of certain types of fluids for stimulation of the production of hydrocarbon deposits, displacing fluids in the well, and for performing cleaning operations on the well production conduit and the like. In this regard, it is known to insert or inject a continuous length of relatively thin walled steel tubing into the well conduit from a large reel or spool on the surface. The forces required to inject or insert and to withdraw several thousand feet of tubing are substantial and various types of apparatus have been developed to perform this function.
As with other types of equipment used in the development and production of wells and in the rugged environment normally encountered in such work, there is an ever present need to increase the handling and performance capabilities and the reliability of such equipment without increasing its mechanical complexity. For example, in regard to tubing injection equipment the preferred concept comprises the provision of a pair of opposed endless flexible conveyor members or chains which are arranged to have elongated runs substantially parallel to each other and between which the tubing is straightened and propelled generally downward through a wellhead and into the well proper. It is, of course, necessary to provide a substantial gripping force on the tubing to perform the injection and withdrawal operations. In this regard, there has been a need to improve the general arrangement of and control of the endless conveyor chain or tubing gripper assemblies so that sufficient gripping forces may be applied uniformly along the opposed runs of the conveyor chains and whereby the gripping forces may be selectively controlled and equalized along the line of contact. Prior art tubing injection assemblies have been characterized by quite complicated arrangements of support rollers and actuator members for applying a biasing force against the opposed conveyor chain courses or runs which are engageable with the tubing. Moreover, prior art tubing injection apparatus have not provided for reliable and automatic compensation of chain tensioning to prevent chain breakage and to compensate for chain elongation.
Another problem assoicated with prior art tubing injector units pertains to the relatively heavy and complex framing or supporting structure associated with the endless chain assemblies. The type of equipment to which this invetion is directed must be highly portable and easily handled, and the reduction in the weight of the injector unit itself is very important in the overall approach to apparatus design.
Another desirable feature in tubing injector equipment pertains to the capability of the unit to handle more than one size or diameter of tubing. Since it is often necessary to change tubing size in order to fit the tubing within a certain size conduit or in order to increase the fluid handling capacity of the tubing, it is advantageous to be able to adapt the injector unit to handle the different tubing sizes.
Still another problem associated with the development of tubing injector apparatus is in the provision of means for guiding the tubing as it is uncoiled from the supply reel into the path between the gripping and conveying chain members so that the tubing is not substantially bent or kinked as it is paid off the supply reel and oriented for engagement with the opposed conveyor chain assemblies.
The aforementioned problems associated with prior art apparatus and desiderata realized from past experience with tubing injector apparatus are dealt with by the present invention which provides improved tubing injection apparatus having a number of important features.